The goal of this R21 is to study of effect of mechanical deformation of the extracellular matrix (ECM) on the] collagenolytic and gelatinolytic degradation of fibrillar triple-helical type-I collagen by collagenase-1 (MMP-1) and gelatinase A (MMP-2). Collagen degradation is necessary for normal musculoskeletal development and ECM maintenance, and it is an important mechanism for ECM degradation in response to trauma, disease and inflammation. The role of mechanical forces in the degradation process, which can act to deform the collagen, are as yet unknown. The conformation of the collagen triple helical molecule, and the tight packing of the collagen molecules into fibrils, effectively restricts the accessibility of the collagenases and gelatinases to the cleavage site within the collagen molecule. It has been proposed that cleavage of the three a-chains at the distinct 3/4-1/4 site is due to a discontinuous and loose microstructural arrangement of the three alpha-chains such that intrinsic chemical forces generated by the collagenase molecule unwind the triple helices to expose them to the catalytic domain of the MMPs. Based on these observations, we hypothesize that mechanical forces that result in deformation of the collagen fibrils which decrease the intra and intermolecular conformational space between the triple helical alpha-chains of the collagen molecule will make the molecule less susceptible to cleavage by the collagenases and gelatinases, while mechanical deformations that increase these openings will make the molecule more susceptible to cleavage. We further hypothesize that specific components of the ECM, specifically the proteoglycan and collagen cross-links, function to attenuate the effects of the mechanical deformation on enzyme cleavage of the collagen molecule. The specific aims of this proposal are to determine the effect of static tensile deformation on the enzymatic cleavage of collagen by collagenase-1 and gelatinase A, and how the proteoglycan component and triple-helical cross-links affect the collagenolytic process. To test these hypotheses we will mechanically strain a single bundle of type I collagen fibrils (rat tail tendon), experimentally measure the enzyme-induced mechanokinetic stress-relaxation response due to MMP-1 or MMP-2, and calculate the enzyme mechanokinetic relaxation function, tau/epsilon, a measure of the rate of collagenolytic activity as a function of mechanical deformation. The findings from this study could fundamentally change our concepts of matrix enzyme function and the design of intervention approaches to include the effect the mechanical environment has on the ECM.